1. Field of the Invention
The present invention relates generally to the production of luminescent display screens for video display devices, and more particularly to the production of luminescent display screens using meniscus coating techniques for the placement of photosensitive screen element slurries on the screening surface of the faceplate of the video display such as may be found, for example, on color cathode ray tubes (CRTs).
2. Discussion of the Related Art
In the art of CRT screen application there are known many forms of screen deposition. Among these are the well-known photolithographic techniques for color screen formation wherein photosensitive slurries containing the luminescent phosphors are spin coated into films on the faceplate and exposed to light wavelengths actinic to the photosensitive slurry, whereupon the exposed pattern of slurry is washed and baked. In color CRT screens serial light exposures are made to form each of the grille, or black matrix, pattern and red, green and blue phosphor patterns hereinafter generically referred to as "screen elements".
Spin coating requires prewetting of the screening surface and can result in slurry waste, uneven coating thickness, and panel skirt or mask support contamination. Elimination of mask support contamination is especially important for high yield production of tensed-foil shadow mask type CRTs having their mask support structures attached directly to the faceplate, as in the flat tension mask (FTM) CRTs made by the assignee hereof. Also, phosphor content of the slurry must be matched to spin-coating technique in order to provide for uniform phosphor content in the resultant spun film on the faceplate. Currently this limits phosphor content of the slurry to about twenty-five to thirty percent by weight to achieve good phosphor distribution. A higher phosphor content would, of course, result in a brighter screen display.
As a great deal of production process knowledge and equipment for photolithographic display screen production is known and currently available, this technique would be much improved by finding a more efficacious method of applying the screen element slurries to the faceplate. Past attempts to improve slurry application include U.S. Pat. No. 3,876,465 to Prazak, III, which details several drawbacks to spin coating. The coating apparatus disclosed by the Prazak III, patent itself can suffer from imprecise coating thickness control and possible mask support structure contamination from slurry particles.
Therefore, it will be seen that of the known methods for photosensitive screen slurry deposition all have drawbacks in relation to uneven coating thickness which may effect brightness uniformity, the uneconomical waste of materials, and possible slurry contamination of mask support structures leading to charged particle contamination of the finished CRT if left uncorrected.
As per the above discussion, there exists a desiderata in the display industry for a reliable, high quality, even thickness screen element application with a minimum of material waste in the production of CRT phosphor screens.
It is therefore among the objects of the present invention to provide such a system for the production of video display screens through the use of known multiple exposure photolithographic techniques in conjunction with improved placement of photosensitive slurries to provide for accurate phosphor screen pattern production with a minimum waste of the screen materials and reduced possibility of subsequent particulate contamination of the screen, shadow mask or finished display device.